This article proposes two linear regression models on cost variation of hospitalization (based on data from the Brazilian National Unified Health System - SUS) for two types of injuries: head trauma and related cases (n = 98,156); fire arm injuries and related cases (n = 8,970). Data were collected from the 1997 standardized Hospital Admittance Forms covering all of Brazil. Explanatory variables were gender, age, hospital administration model (public, private, etc.), region of the country, hospitalization in a capital city, use of ICU, surgery, death, duration of hospitalization, most frequent procedures, special procedures, and interaction among certain variables. The two models adjusted well, with R2 = 0.7264 for the first and 0.7663 for the second. Explanatory variables in the first model were all significant, and only three variables in the second failed to show statistical significance. The two main variables in both models were use of ICU and surgery. Diagnostics for detection of outliers, multicolinearity, model specification error, and homoscedasticity were performed.